442 A Reply to Mr. Carr's Letter, 



of ammonia, in great quantity, and its judicious application 

 to agricultural purposes, are processes of' very great impor- 

 tance to the landed interest. 



LXXVITI. Geological Observations on the Excavation of 

 Valleys, and local Denudations of the Strata of the Earth 

 in particular Districts, &c, in Reply to Mr. John 

 Carr's Letter in the last Number, p. 385. By Mr. John 

 Farey. 



" It is only from the itinerant geologist cautiously pacing over various and 

 extensive districts, and marking with experienced intelligence the wonderful 

 phenomena which every where present themselves, that we can hope to ob- 

 tain that accumulation of practical facts which can alone guide us to a sober 

 and correct theory of the natural causes which, at remote periods, have ope- 

 rated those stupendous changes which are every where seen on and near the 

 surface of our globe*." John Carp.. 



To Mr. Tilloch, — Sir, 

 A. wet morning, which seems to threaten an interruption 

 of some hours' duration, to my researches in the highly in- 

 teresting district which surrounds this town (Sheffield in 

 Yorkshire), presenting the opportunity of looking into the 

 last Number of the Philosophical Magazine, I have been 

 induced to trouble you with a few lines, in explanation of 

 some points, which your able correspondent Mr. John Carr 

 of Manchester has touched upon in his Letter therein. In 

 the present state of geological knowledge, nothing can be 

 more just than the introductory remark of Mr. Carr, which 

 I have quoted above, as to the class of persons who are at 

 this juncture most likely to trace out and discover the natu- 

 ral causes which have operated, in effecting the present state 

 and condition of the earth ; arising from the circumstance, 

 that very few, of the great and leading/ac/s appertaining to 

 the crust of the earth have yet been touched upon, much 

 less have they been so fully treated on or illustrated by geo- 

 logical writers, that " the closet geologist" can, over an 

 ** accumulation of practical facts," sit down, and deduce 

 ff a sober and correct theory," or even judge of the truth or 

 • Vide p. S35. 



otherwise^ 



